Methods for wildlife monitoring in tropical forests: Comparing human observations, camera traps, and passive acoustic sensors od Zwerts, JA, Stephenson, PJ, Maisels, F, Rowcliffe, M, Astaras, C, Jansen, PA, van Der Waarde, J, Sterck, LEHM, Verweij, PA, Bruce, T, Brittain, S, van Kuijk, M